Leafy Greens Good for the Eyes Also Boost Kids' Brain Function

Batya Swift Yasgur, MA, LSW

June 30, 2017

Higher levels of retinal carotenoids are associated with superior academic achievement and increased efficiency in performing cognitive tasks, new research shows.

A team of investigators led by Naiman Khan, PhD, RD, professor of kinesiology and community health, together with Anne Walk, PhD, postdoctoral scholar, both of the University of Illinois at Urbana-Champaign, conducted two studies that used macular pigment optical density (MPOD) to measure concentrations of lutein and zeaxanthin, both of which are retinal carotenoids in the eyes.

In one study, researchers measured MPOD in 56 children (aged 8 to 9 years), assessed their academic performance, and measured their 3-day dietary intake of lutein and zeaxanthin.

They found that retinal lutein and zeaxanthin are positively related to academic achievement in children, even when controlling for other factors, such as aerobic fitness, body composition, and intelligence quotient (IQ).

Another study investigated the relationship between MPOD and performance on a challenging cognitive task in 49 children (aged 8 to 10 years).

The researchers found that children with higher MPOD responded to cognitive tasks more efficiently, especially in tasks requiring attention control. The finding provides "novel support" for the neuroprotective influence of retinal carotenoids during preadolescence.

"Lutein is known to accumulate in the retina and several other regions of the brain and has been shown to protect against eye disease and preserve cognitive function in older adults. These studies are important because they demonstrate that the beneficial influence of lutein on cognition is evident in childhood," Dr Khan told Medscape Medical News.

"We also know that these pigments are found in high quantities in the infant brain. That suggests that they are important in some way for brain development," Dr Walk said in a release.

The first study was published online May 23 in Nutritional Neuroscience. The second study was published in the August issue of the International Journal of Psychophysiology.

Improved Academic Performance

In both studies, the investigators note that previous research has demonstrated the potential role of lutein and zeaxanthin in combating cognitive decline in the elderly. However, much less is known about the potential cognitive-enhancing or neuroprotective effects of these carotenoids in children.

Prior studies have shown that both lutein and zeaxanthin are found in the infant brain, with a preferential accumulation of lutein. In fact, "the relative contribution of lutein to the total carotenoids found in infant brains is almost two-fold greater than in adults, accounting for 59% vs 34% respectively, suggesting a selective role of lutein in early neural development."

To investigate the potential impact of retinal carotenoids on cognition in children, the researchers in both studies drew participants from FITKids, an ongoing large, longitudinal, randomized controlled trial of an intervention involving physical activity in children.

Both studies measured MPOD because it is indicator of retinal xanthophylls, it is a correlate of brain lutein level, and it is a "good proxy" for the amount of lutein and zeaxanthin in the brain. Moreover, assessment of MPOD is noninvasive.

Dr Khan's team evaluated participants (n = 49) on 2 days. On the first day, the children were asked to complete the Woodcock Johnson Tests of Cognitive Abilities to provide an estimate of IQ and were administered the Kaufman test of Academic and Educational Achievement II (KTEA II) to assess scholastic achievement.

The height and weight of the children were measured, and a maximal oxygen consumption (VO2max) test was used to assess aerobic fitness. Legal guardians provided information regarding the children's demographics, health history, and pubertal timing.

After the first visit, the children were given forms on which to record at home the food they consumed during a period of 3 days.

At the second visit, the children completed an assessment of body composition via dual-energy X-ray absorptiometry. At both visits, MPOD was assessed. The researchers averaged the two MPOD values and utilized stepwise hierarchical regression models to determine the relationship between the averaged MPOD and academic achievement tests, following adjustments of the key covariates (eg, sex, aerobic fitness, body composition, and IQ).

The researchers found a positive correlation between the dietary intake of lutein and zeaxanthin and MPOD (r = 0.39; P = 0.02).

On bivariate correlation analysis, IQ, VO2max, and fat-free mass VO2max positively correlated with the achievement composite score (r = 0.62, P < .01; r = 0.33, P = .01; and r = 0.26, P = .05, respectively).

BMI and whole-body percent fat were negatively correlated with the achievement composite score (r = − 0.37, P < .01; and r = − 0.30, P = .03, respectively).

The regression analyses found that MPOD improved the model for overall academic achievement (ΔR2 = 0.10, P < .01), mathematics (ΔR2 = 0.07, P = .02), and written language composite standard scores (ΔR2 = 0.15, P < .01), even beyond the covariates.

"The major finding was that children with higher MPOD values have superior performance on academic measures, particularly in math and written language," the researchers write.

The findings highlight "the importance of habitual intake" of lutein and zeaxanthin for improved academic performance, they add.

"These findings were not surprising to us," said Dr Khan. "We had hypothesized a positive relationship between lutein in the eye and children's cognitive function and academic abilities."

Antioxidant Effect?

Dr Walk's team examined children's cognitive performance (response accuracy and reaction time) by using a modified version of the Eriksen Flanker Task, a cognitively challenging activity in which participants respond to the directionality of a centrally located image of a target fish that is presented amid several images of task-irrelevant distractor fish that are either congruent (facing the same direction) or incongruent (facing the opposite direction).

The researchers recorded the children's electroencephalographic (EEG) activity during the task — in particular, the P3 component of the event-related potential (ERP) waveform.

Participants underwent two testing sessions. During the first, legal guardians completed a questionnaire about demographic and health information. During the second, participants completed the EEG-recorded cognitive tasks. MPOD was assessed at both sessions, and the values were averaged.

When bivariate correlational analyses were performed, the researchers found that flanker response accuracy was significantly related to MPOD values for incongruent trials but was only moderately related for congruent trials (r = .341, P = 0.017, confidence interval [CI] = .124, .542; and r = .243, P = 0.093, CI = .024, .454, respectively).

MPOD was not related to mean reaction time (r ≤ 106, P ≥ .235). The confidence intervals for the significant and moderate correlations did not span 0, "suggesting reliable moderate correlations," the researchers write.

"These results indicate that children with higher MPOD values were more likely to exhibit high performance on the flanker task and that this was particularly evident when greater levels of attentional control were demanded," they write. However, higher MPOD values did not increase the speed of performing the task.

"The hypothesis that MPOD values would be positively related to flanker task performance was supported. Thus, the beneficial effects of retinal carotenoids appear to have global benefits in cognitive control processing, though the greatest benefit is observed when cognitive control demands are higher," the authors write.

The investigators add that these data did not show a significant relationship between MPOD and reaction time, "indicating that the benefits of lutein on cognitive control have a preferential effect of accuracy as opposed to processing speed in children."

Discussing these findings, Dr Khan suggested that "a potential mechanism of the neurocognitive benefits of lutein and zeaxanthin may be the antioxidant effects of lutein, which may extend beyond the eye and protect brain tissue as well.

"It is also possible that lutein facilitates the neuroprotective effects of other nutrients thought to be beneficial to cognitive function and brain health, such as docosahexaenoic acid." However, he cautioned, "additional research is needed to determine the exact mechanism by which lutein impacts the brain and cognitive function."

Encourage Healthy Eating

Commenting on the studies for Medscape Medical News, Elizabeth Johnson, PhD, of the Jean Mayer USDA Human Nutrition Center on Aging, Tufts University, Boston, Massachusetts, said the studies "are consistent with what we know about lutein and zeaxanthin from intervention studies in adults, which is that when you increase these dietary components, you improve cognitive function."

She cautioned that the "findings can only demonstrate association rather than cause and effect."

Nevertheless, the studies are valuable and "of particular interest because lutein and zeaxanthin are not considered 'essential' nutrients," so "there are no policies requiring that school lunch programs must contain a certain amount of them."

However, "although these are not 'essential,' they are beneficial, so it is important to look at phytonutrients in plants, fruits, vegetables, and nuts and advise people what their targets should be to ensure optimal health."

She advised psychiatrists to inquire about the nutrition of their patients. "If a person is eating to improve brain function, it will also help overall health because it is the same diet — fruits, vegetables, low fat, good fat, the appropriate number of calories, and exercise ― which is good for the brain and everything below the brain as well."

Dr Khan added that "encouraging children to eat more foods rich in lutein, like leafy greens and fruits, might improve the cognitive status of children, and certainly will not hurt."

This research is part of a larger randomized controlled trial supported by the National Institutes of Health and Abbott Nutrition via a Center for Nutrition, Learning, and Memory grant to the University of Illinois. Dr Khan and Dr Walk have disclosed no relevant financial relationships.

Nutr Neurosci. Published online May 23, 2017. Abstract

Int J Psychophysiol. 2017;118:1-8. Abstract

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